Permanent magnets, particularly Nd—Fe—B sintered magnets (so-called neodymium magnet) are made of a combination of iron with elements of Nd and B that are low-priced and abundant as natural resources and also capable of stable supply and, thus, can be manufactured at a low cost and, at the same time, have high magnetic properties (maximum energy product is about 10 times that of ferritic magnets). Therefore, they are used in various kinds of electronic products and are recently widely used in motors and generators for hybrid cars.
As an example of manufacturing Nd—Fe—B sintered magnets, there is known a powder metallurgy method. In this method, Nd, Fe and B are first mixed in a predetermined composition ratio, dissolved, and molded to manufacture an alloy raw material. It is once coarsely crushed by, e.g., hydrogen crushing step, and is subsequently finely ground by, e.g., jet mill fine grinding step, thereby obtaining an alloy raw meal powder. Then, the obtained alloy raw meal powder is subjected to orientation in the magnetic field (magnetic field orientation), and is compression-molded while being charged with magnetic field, thereby obtaining a molded body. Then, the molded body is sintered under predetermined conditions to thereby manufacture a sintered magnet.
As a method of compression molding in the magnetic field, there is generally used a uniaxial pressurizing type of compression molding machine. In this compression molding machine, alloy raw meal powder is filled into a cavity formed in a penetrating hole in a die, and is pressurized (pressed) by a pair of upper and lower punches from the upper and lower directions to thereby form a product out of the alloy raw meal powder. There has been a problem in that, at the time of compression molding by means of the pair of punches, high orientation cannot be obtained and that the magnetic properties cannot be improved due to friction among the particles of the alloy raw meal powder filled in the cavity or due to friction between the alloy raw meal powder and the wall surface of the mold set in position in the punch.
In view of the above, there is known another compression molding method in which, after having filled a cavity with alloy raw meal powder, at least one of punches of an upper punch and a lower punch is vibrated in the direction of pressurizing (pressing direction) at the time of magnetic field orientation. This compression molding method is performed in the following manner, i.e., by charging magnetic field while alloy raw meal powder is vibrated by the upper punch or the lower punch, the friction among the particles in the alloy raw meal powder filled in the cavity is changed from the static friction to the dynamic friction. The friction among the particles of the alloy raw meal powder is thus reduced with a consequent improvement in the flowability of the alloy raw meal powder. Since the raw meal powder can thus be moved so as to be arrayed in the direction of magnetic field orientation, the orientation can be improved (see patent document 1).    Patent Document 1: International Publication No. 2002-60677, see e.g., claims)